A computer network is a collection of interconnected computing devices that can exchange data and share resources. In a packet-based network, such as an Ethernet network, the computing devices communicate data by dividing the data into variable-length blocks called packets, which are individually routed across the network from a source device to a destination device. The destination device extracts the data from the packets and assembles the data into its original form.
Certain devices, referred to as routers, maintain routing information representative of a topology of the network. The routers exchange routing information so as to maintain an accurate representation of available routes through the network. A “route” can generally be defined as a path between two locations on the network. Upon receiving an incoming data packet, a router examines information within the packet, often referred to as a “key,” to select an appropriate next hop to which to forward the packet in accordance with the routing information.
A variety of routers exist within the Internet. Network Service Providers (NSPs), for example, maintain “edge routers” to provide Internet access and other services to the customers. Examples of services that the NSP may provide include Voice over IP (VoIP), access for Asynchronous Transfer Mode (ATM) or frame relay communications, Internet protocol (IP) data services, and multimedia services, such as video streaming. The edge routers of the NSPs often communicate network traffic to high-speed “core routers,” which may be generally viewed as forming the backbone of the Internet. These core routers often include substantially more processing resources than the edge routers, and are designed to handle high volumes of network traffic.
NSPs often desire to isolate the forwarding functions and other networks services for customers from one another for purposes of reliability and security. As a result, in some environments an NSP may implement many dedicated routers and other networking devices for each different enterprise customer. However, the complexities associated with maintenance and management of separate routers and other networking equipment can be significant.
To address these concerns, some conventional routers allow an NSP to configure and operate multiple logical software routers within the same physical routing device. These software routers are logically isolated in the sense that they achieve operational and organizational isolation within the routing device without requiring the use of additional or redundant hardware, e.g., additional hardware-based routing controllers. That is, the software routers share the hardware components of the physical routing device, such as the packet forwarding engine and interface cards. However, this solution has limitations and may be undesirable in certain situations. For example, multiple software routers executing within the same physical routing system have scaling limitations as each software logical router is affected by the scaling requirements of every other software logical router in the system. That is, since the software routers share the same hardware, kernel, and forwarding components, any increase in state (e.g., routing information and forwarding tables) for one of software routers may degrade the performance of the other software routers. Thus, the software routers cannot be scaled independently from one another as the needs of one customer grows while the needs of the other customers may remain unchanged. Software logical routers have other limitations such as fate sharing of the common kernel and forwarding components, and the limitation that the routers must inherently use the same version of any shared hardware or software component.